Developer Max Rudberg suggests that users could squeeze the sides of their iPhone to close apps. He writes:

This could be a real wow effect. Seeing how the phone reacts to your grip and then having the app vanish in the palm of your hand.

To avoid ‘squeeze to go Home’ from happening by accident, a visual cue could show that pressure is being applied. In this concept, the app begins to shrink to reflect the pressure that is being applied. When the pressure goes over a defined threshold, the user is returned to the Home screen.

The strength of a users grip will of course vary. Therefore, a setting for how much pressure that’s needed before an app is exited could be a good idea.”